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Monitoring lithium batteries


Dr Bob

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53 minutes ago, cuthound said:

 

I was led to believe that is heat whilst charging that kills phone and laptop batteries early.

 

Some people leave them on charge for hours even when they are charged.

Probably cheap charge controllers that are still providing a small charge.    Think e-cigs and their exploding batteries.

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4 hours ago, George and Dragon said:

Ah, the well known phenomenon of London's weather being the weather for the whole country. I understand how this misconception comes about - in the same way that London's news is the news for the whole country

You are so right. About let's say ish ten million people live in the great crap whole known as Greater London which means they are in a minority as ish fifty million of us don't live there and in fairness would never live there for all the tea in China but the Wallies of the media always quote London ?

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11 minutes ago, mrsmelly said:

You are so right. About let's say ish ten million people live in the great crap whole known as Greater London which means they are in a minority as ish fifty million of us don't live there and in fairness would never live there for all the tea in China but the Wallies of the media always quote London ?

Have you tried telling them, it's easier pushing string.

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Battery wise how about these alternator ready fancy batteries https://www.alpha-batteries.co.uk/12v-100ah-relion-lithium-battery/?gclid=CjwKCAjwns_bBRBCEiwA7AVGHv0SnzGwV1qlLRnbTzQ6LShetyQI8d1K15hM4Abn47Z9J9goneQvphoCsiAQAvD_BwE 

 

By my reading they are a direct fit to motorhomes where they are charged by the alternators ok in comparison to mine they are expensive but as more use them they will get cheaper one assumes

Edited by peterboat
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7 minutes ago, peterboat said:

Battery wise how about these alternator ready fancy batteries https://www.alpha-batteries.co.uk/12v-100ah-relion-lithium-battery/?gclid=CjwKCAjwns_bBRBCEiwA7AVGHv0SnzGwV1qlLRnbTzQ6LShetyQI8d1K15hM4Abn47Z9J9goneQvphoCsiAQAvD_BwE 

 

By my reading they are a direct fit to motorhomes where they are charged by the alternators ok in comparison to mine they are expensive but as more use them they will get cheaper one assumes

Max Continuous Discharge: 1C=100A

 

So no use for any combined loads over 1200W.  

 

And 950 quid!  that's the problem with having a BMS built into each battery, and why what I would want is a separate BMS/charge controller and plain LFP batteries.  I suspect it would only be a variant of the A2B or B2B boxes, but I would want one that can handle more than 200A.

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4 minutes ago, TheBiscuits said:

Max Continuous Discharge: 1C=100A

 

Even odder, is the auto over-voltage cut off specified of 16v, and the under voltage cut-off of 8v. 

 

If either value is actually hit or even approached, the cells are dead meat according to Jono and the American bloke whose name mo-one seems to know!

 

Perhaps they mean the post terminal voltage on the outside of the 'battery' rather than the actual cell voltage inside.

 

Another thing is none of the RELiON literature says whether they contain four large single cells or a grid of hundreds of tiny cells.

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My worry is how reliable is the BMS?

 

If it goes faulty then it could easily trash the expensive lipo4 batteries.

 

I think I will wait at least another 5 years before buying any, and learn from other people experience.

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4 minutes ago, cuthound said:

 

 

I think I will wait at least another 5 years before buying any, and learn from other people experience.

Very very wise words, but make it 20 years and they may be worth looking at.

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On 15/08/2018 at 13:15, peterboat said:

Battery wise how about these alternator ready fancy batteries https://www.alpha-batteries.co.uk/12v-100ah-relion-lithium-battery/?gclid=CjwKCAjwns_bBRBCEiwA7AVGHv0SnzGwV1qlLRnbTzQ6LShetyQI8d1K15hM4Abn47Z9J9goneQvphoCsiAQAvD_BwE 

 

By my reading they are a direct fit to motorhomes where they are charged by the alternators ok in comparison to mine they are expensive but as more use them they will get cheaper one assumes

Spent a bit of time today looking at the pdf information on the RB100. Some interesting graphs....see below.

The first one shows voltage and SoC rising, I assume at a charging rate of 20A for the 100A battery. If I am reading this correctly, you should be able to monitor voltage rise and stop charging at 13.8V (as Peter told us) with between 80 and 90% SoC, before you get to the top 'knee' and before you get to the overcharge scenario. Setting a solar charger to have an absorption voltage of 13.8V and a float of 13.4V would therefore surely work, unless it needed to be physically disconnected at 13.8V.

 

The second graph is an interesting one showing number of cycles which depend on DoD. I had envisaged the best strategy for me...to give best lifetime ....was to operate between 20 and 80% SoC but the graph shows number of cycles to decrease with DoD so would  20-80% SoC would be significantly worse than 40-100% SoC? This graph would suggest it maybe. Is this why Victron are pushing the 50-100% range?

Screen Shot 2018-08-17 at 17.23.11.png

Screen Shot 2018-08-17 at 17.24.17.png

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33 minutes ago, Dr Bob said:

 

The second graph is an interesting one showing number of cycles which depend on DoD. I had envisaged the best strategy for me...to give best lifetime ....was to operate between 20 and 80% SoC but the graph shows number of cycles to decrease with DoD so would  20-80% SoC would be significantly worse than 40-100% SoC? This graph would suggest it maybe. Is this why Victron are pushing the 50-100% range?

 

 

I don’t think you can extrapolate that data from the graph. The graph has the premis that one is starting from fully charged. We know that both over charge and over-discharge are life shorteners so I doubt that 20-80 would be any worse than 40-100%. You still have your lead acid head on!

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6 minutes ago, nicknorman said:

 The graph has the premis that one is starting from fully charged.

 

I agree Nick, so just a guess from me if working at the bottom end is worse. It would be good to get some facts on this point. It sounds like storing Li's at 30% SoC is optimim so maybe the bottom end is good....although is that just for safety?

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1 hour ago, Dr Bob said:

Setting a solar charger to have an absorption voltage of 13.8V and a float of 13.4V would therefore surely work, unless it needed to be physically disconnected at 13.8V.

My understanding from the Yank-with-no-name is that it needs to be completely disconnected, however Victron talk about a float charge so I’m not clear on this myself. 

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25 minutes ago, WotEver said:

My understanding from the Yank-with-no-name is that it needs to be completely disconnected, however Victron talk about a float charge so I’m not clear on this myself. 

Presumably if the float voltage matches the resting voltage then no current will flow and the battery can’t know it is on float. But if a load is placed on the batteries then the charger will start to supply current. Or if the float voltage is set to say the resting voltage at 80% SoC then current will only flow once the SoC falls a bit, which is probably a better idea.

 

One of the problems is that a degree of anticipation is needed during charging. So for example, if you are boating for 8 hours and the batteries are fully charged after 2 hours, what you really want to do is to charge only to 80%, then drop to float or disconnect, then 30 mins or an hour before you plan to shut down, press a button to kick the charging system back into life to take the batteries up to 100%. ... Unless you are returning to the marina in which case you want to leave it at 80%.

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2 hours ago, nicknorman said:

Presumably if the float voltage matches the resting voltage then no current will flow and the battery can’t know it is on float. But if a load is placed on the batteries then the charger will start to supply current. Or if the float voltage is set to say the resting voltage at 80% SoC then current will only flow once the SoC falls a bit, which is probably a better idea.

Yup, that all makes sense. 

2 hours ago, nicknorman said:

One of the problems is that a degree of anticipation is needed during charging. So for example, if you are boating for 8 hours and the batteries are fully charged after 2 hours, what you really want to do is to charge only to 80%, then drop to float or disconnect, then 30 mins or an hour before you plan to shut down, press a button to kick the charging system back into life to take the batteries up to 100%. ... Unless you are returning to the marina in which case you want to leave it at 80%.

I think you’re over-complicating it although I do see your point. Simpler surely to only ever take them up to 80%. Discharge to 20% and you have 60% usable which is more than you’d want to take from a similarly sized LA, plus it is able to be replenished relatively quickly. 

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31 minutes ago, WotEver said:

 

I think you’re over-complicating it although I do see your point. Simpler surely to only ever take them up to 80%. Discharge to 20% and you have 60% usable which is more than you’d want to take from a similarly sized LA, plus it is able to be replenished relatively quickly. 

Because otherwise I’ve paid for 20% capacity that I can never use. I am from Aberdeen, you know! (Well not from birth, but never mind!).

 

Anyway, you say “over complicate” but really, whilst these things might be difficult to set up initially, once you have done that (and provided it is literally just a “charge boost” button to press), it isn’t complicated in day to day usage.

 

Our boat is full of “over complication”. Most people have a switch for their shower drain pump. We don’t, we have a flow switch in each of the hot and cold pipes going to the shower mixer, wired in parallel to the input of a computer. When activated by turning the shower tap on, an FET turns the drain pump on. When the tap is turned off, a timer keeps the FET on for 20 seconds, then turns it off. Very complicated but the day to day consequence is that you just turn the shower on, have your shower, and the draining looks after itself.

 

My point is that there is an important discrimination between complication of design and complication of use.

Edited by nicknorman
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Just now, nicknorman said:

Because otherwise I’ve paid for 20% capacity that I can never use. I am from Aberdeen, you know! (Well not from birth, but never mind!)

Ahh yes, I was overlooking the cannyness...

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In CC land, how much of an issue is charging to 100% soc?

Batteries are 100% two hours into a 6 hour cruise, as soon as I tie up and turn the engine off (subject to no other charging sources ie. solar) I'm using power and will soon be at 95% or lower as long as the bank capacity is sized to my power requirements.

Yes when and if I leave the boat, say for a couple of weeks in a marina, I need to scrub 20% off fully charged batteries before everything is isolated and I leave the boat.

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1 minute ago, PMB said:

In CC land, how much of an issue is charging to 100% soc?

Batteries are 100% two hours into a 6 hour cruise, as soon as I tie up and turn the engine off (subject to no other charging sources ie. solar) I'm using power and will soon be at 95% or lower as long as the bank capacity is sized to my power requirements.

Yes when and if I leave the boat, say for a couple of weeks in a marina, I need to scrub 20% off fully charged batteries before everything is isolated and I leave the boat.

Not much of an issue I’d suggest, so long as for the remaining 4 hours of the cruise you don’t overcharge the batteries.

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13 minutes ago, PMB said:

In CC land, how much of an issue is charging to 100% soc?

Batteries are 100% two hours into a 6 hour cruise, as soon as I tie up and turn the engine off (subject to no other charging sources ie. solar) I'm using power and will soon be at 95% or lower as long as the bank capacity is sized to my power requirements.

Yes when and if I leave the boat, say for a couple of weeks in a marina, I need to scrub 20% off fully charged batteries before everything is isolated and I leave the boat.

I recently left my boat at Goole for two weeks, it has 1 KW of solar I left the fridge freezer running and the fan on the composting toilet on, when we returned the batteries were sitting at 13.6 volts because my Midnite controller is set at this. Now I chose 80% because it gives the best mix between battery life and usable power, I have 4 x 138 ah batteries which for my needs is enough especially as this summer my batteries have been full by late morning just using solar. 

The next stage of my conversion will be to remove the diesel engine and replace it with an electric motor powered by 10 of the valence batteries [ 2 x 5 in series to give me 60 volts which is really 69 volts at 80%] these will be charged by a new bigger solar array [3 KW] in the summer when not moving they will be switched to an immersion heater, in the winter they will 2KW will be used for domestic. My system uses the solar in the day to provide motive and domestic power the batteries are just for dull days, night time use and emergencies

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16 hours ago, nicknorman said:

Not much of an issue I’d suggest, so long as for the remaining 4 hours of the cruise you don’t overcharge the batteries.

Presumably that don't 'overcharge' is really don't 'go over voltage' ie less than 3.6v per cell

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16 hours ago, peterboat said:

I recently left my boat at Goole for two weeks, it has 1 KW of solar I left the fridge freezer running and the fan on the composting toilet on, when we returned the batteries were sitting at 13.6 volts because my Midnite controller is set at this. Now I chose 80% because it gives the best mix between battery life and usable power, I have 4 x 138 ah batteries which for my needs is enough especially as this summer my batteries have been full by late morning just using solar. 

The next stage of my conversion will be to remove the diesel engine and replace it with an electric motor powered by 10 of the valence batteries [ 2 x 5 in series to give me 60 volts which is really 69 volts at 80%] these will be charged by a new bigger solar array [3 KW] in the summer when not moving they will be switched to an immersion heater, in the winter they will 2KW will be used for domestic. My system uses the solar in the day to provide motive and domestic power the batteries are just for dull days, night time use and emergencies

Sounds an interesting build. My one is going the opposite way. After 7 years CCing with 400w solar, new build will be LiFePO4 charged with a fairly trad engine and no solar at all. Probably mostly Victron kit. I hope to pop over to Onboard Energy next week to quiz them further as most of my email questions like; how to turn off alternator to avoid too long a charge at acceptable voltage level, have met the "The victron BMS takes care of all that". All well and good but when the whole system will cost nearly as much as a FP genset I'd like a bit more detail.

 

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19 minutes ago, PMB said:

Sounds an interesting build. My one is going the opposite way. After 7 years CCing with 400w solar, new build will be LiFePO4 charged with a fairly trad engine and no solar at all. Probably mostly Victron kit. I hope to pop over to Onboard Energy next week to quiz them further as most of my email questions like; how to turn off alternator to avoid too long a charge at acceptable voltage level, have met the "The victron BMS takes care of all that". All well and good but when the whole system will cost nearly as much as a FP genset I'd like a bit more detail.

 

If your needs are no more than 200amp (like a 2kw inverter) and have a 100amp or less alternator the Victron BMS12/200 seems to be the good option as the batteries are directly connected through this.   The other BMS is more of a remote controller that tells chargers and loads to turn off.   For a alternator this would be connected to the starter batteries and the BMS controls the split charge relay.

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